5 Bake 18 to 20 minutes or until cake springs back when touched lightly in center and begins to pull away from side of pan. Cool 10 minutes. Remove from pans to cooling racks; cool completely.

6 Wash cake pans. Bake and cool remaining 3 cake layers as directed.

7 In large bowl, beat shortening and butter with electric mixer on medium speed until light yellow. On low speed, gradually beat in powdered sugar. Beat in vanilla. Add milk, 1 tablespoon at a time, beating until frosting is smooth. Beat on high speed until light and fluffy.

8 Trim rounded tops off cakes to level, if needed. On serving plate, place purple cake layer. Spread with frosting to within 1/4 inch of edge. Repeat with blue, green, yellow, orange and red cake layers. Spread light coat of frosting on top and side of cake to seal in crumbs, then frost with remaining frosting.

Notes

For a deeper red color, add a teaspoon or two of unsweetened baking cocoa to the red batter